Under Windows 7 OS,we are connected remotely when log-off remote client or switch user on remote client, UltraVNC will close automaticly. This was not happening in Windows XP.Anyone has ideal how to solve this problem?

VNC need to run in the console (visable) session , each time the console session change vnc is restarted.Unless you set a reconnecttime ( viewer option) you manual need to reconnect after each session switch. If reconnect is set, server still restart, but connection is done in background without the need to reenter a password.